Posted by **Adria** on Tuesday, December 8, 2009 at 8:57am.

In a distribution of 400 response times with a mean of 7 minutes and a standard deviation of 2 minutes, the maximum number of response times greater than 13 minutes would be about:

A. 40

B. 100

C. 75

D. 90

- Statistics -
**Reiny**, Tuesday, December 8, 2009 at 9:58am
According to

http://davidmlane.com/hyperstat/z_table.html

the probability of a time greater than 13 minutes is .00135

None of your choices result from that probability.

- Statistics -
**PsyDAG**, Tuesday, December 8, 2009 at 10:06am
Z = (x - μ)/SD

Z = (13-7)/2 = 6/2 = 3

Look up this Z in a table in the back of your statistics text covering areas under the normal distribution for the smallest area. Multiply this value by 400.

Unfortunately, that does not fit any of your choices. Do you have any typos?

- Statistics -
**Adria**, Tuesday, December 8, 2009 at 12:51pm
No. No typos. That's how its written on the packet I am doing. Thank You so much for your help though, I guess my teacher might've made a typo...

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